In a case where a failure has occurred on an overhead transmission/distribution line, the surge signal that occurs due to the failure is detected by a failure-detecting sensor provided on the overhead transmission/distribution line. And, failure standardization for standardizing the inter-failure-region or failing position is conducted by using the difference between each two times at which the surge signals arrive, etc. As a method of detecting the surge signal to determine a relevant failure, there are the method of measuring a line current, line voltage, etc. by using a sensor directly connected to the overhead transmission/distribution line such as a current transformer (CT), a potential transformer for using on gages (PT, PD), etc., the method of measuring a line current, line voltage, etc. by using a noncontact sensor such as a magnetic sensor that detects the magnetic field that occurs due to the electric current and an electric field sensor that detects the electric field that occurs due to the voltage, and so on.
This applicant previously proposed a noncontact sensor that is arranged to be used by being installed on an overhead transmission/distribution line steel tower (refer to, for example, a Japanese official gazette of Japanese Patent Application Laid-Open No. 2003-161755<pages 3-4, FIG. 2>). This is made up into a structure in which an electric-current sensor that detects the change in the spatial magnetic field due to the electric current passing through the overhead transmission/distribution line and that is comprised of a core and coil and a voltage sensor that detects by a plate electrode the line voltage capacitance-divided by the spatial charge between an electrically charged portion of the overhead transmission/distribution line and a plate electrode insulated from the earth, both, are accommodated in a hermetically sealed sensor container. Also, the sensor container consists of a container main body that is formed using a non-magnetic material such as stainless steel and one side of that is opened, and a lid member that hermetically seals the opening portion and that is formed using insulative synthetic resin such as vinyl chloride resin and polyethylene resin. This noncontact sensor is used by being secured to a transmission steel tower side surface in such a manner as the lid-member side comprised of the insulative synthetic resin is opposed to the electrically charged portion of the transmission line that provides a measured phase.